Is it possible to make my ext3fs into an ext2fs without destroying data? Also is it possible to do the reverse without destroying data? The reason I ask is that I want to repartition my disk so that I have 10 gigs of free space for Windows at the beginning of the drive.

Actually there is only little need to do so, because in most cases it is sufficient to mount the partition explicitely as ext2 {as described by craftyc}. But if you really need to convert your partion back to ext2 just do the following on an unmounted {!!!} partition:

tune2fs -O ^has_journal /dev/hdaX

To be on the safe side you should force a fsck run on this partition afterwards:

fsck.ext2 -f /dev/hdaX

After this procedure you can safely delete the .journal file if there was any.